Seawater-resistant alloy of brass or aluminum brass



United States Patent 3,214,269 SEAWATER-RESISTANT ALLOY 0F BRASS 0R ALUMINUM BRASS Brge Lunn, Vanlose, Copenhagen, Denmark, assignor to Aktieselskabet Nordiske Kabel-OG Traadfabriker,

Copenhagen, Denmark No Drawing. Filed Sept. 12, 1963, Ser. No. 308,926 2 Claims. (Cl. 75-153) The present invention relates to a seawater-resistant alloy of brass or aluminum brass, preferably for pipe, sheet, band, and wire material which is prepared by plastic forming.

As construction material for pipe conduits, for example condensator tubes and other apparatus coming into contact with seawater, especially in systems on board ships, there have been proposed a long series of alloys in order to obtain a good resistant against corrosion.

Originally, copper tubes have been used and later on instead thereof brass tubes containing 70 percent copper, 1 percent tin and 29 percent zinc. This alloy is still employed in connection with fresh water but in connection with seawater there have been obtained better results with a brass alloy containing 76 percent copper, 2 percent aluminum, and 22 percent zinc. On account of the tendency of this aluminum brass to dezincification one one has later on begun to use an addition of small quantities of arsenic which counteract the above tendency. A known alloy contains 76 percent Cu, 2 percent Al, 22 percent Zn, and 0.04 percent As.

Copper-nickel alloys have also been employed for the above purposes, especially alloys with a high nickel content of about 30 percent because of the corrosion resistance. However, it has been found that the resistance of these alloys against corrosion is improved considerably by the alloying of 0.5 to 2 percent of iron, even when the nickel content is considerably reduced. Such iron-containing copper-nickel alloys are superior to brass alloys in several respects because the problem of dezincification is eliminated, and because the stress corrosion typical of the brass alloys does not occur, either. However, it is a drawback of the copper-nickel alloys that they are difficult to work and are more expensive than the brass alloys. In addition thereto, the copper-nickel-iron alloys have a tendency to the so-called deposit attack corrosion which is less pronounced as regards the brass alloys.

When aluminum was for the first time introduced into brass, it was thought that this metal formed a corrosionresistant oxide film on the brass surface. However, the presence of the said film has not been proved although the alloy seems to possess a surface layer having considerably greater strength than brass surfaces free of aluminum. This may be demonstrated by measurement of the dielectric potential of the surface layer.

Tubes of copper-nickel, copper-nickel-iron, and aluminum brass which have been exposed to seawater for a prolonged space of time without corrosive attack giving rise to corroding through or the formation of cracks, will show an even fixed corrosion film on the surface contacting the seawater. This corrosion film is character istic in that it consists of deposition layers containing relatively large amounts of iron hydroxide. It is also known "ice to improve the durability of tubes, such as aluminum brass tubes by adding small amounts of iron sulphate or other iron compounds to the water streaming through. Hereby the said deposition layers containing iron hydroxide protecting against corrosive attack of seawater are formed.

It has hitherto been common to employ iron-free aluminum brass alloy for the above purposes because an iron content renders it somewhat more difiicult to work the alloy into tubes or sheets, for example. In the production of molded objects it has been known for several years to employ iron-containing aluminum-manganese brasses, for example, for ship propellers, the iron content adding to the mechanical strength, but such alloys have never gained access for purposes where plastic forming by rolling, pressing, and drawing is employed.

The present invention is based upon the discovery that by employing a relatively high iron content in brass or aluminum brass for alloys destined for plastic forming, especially for pipe, sheet, band, and wire material, particularly condensator tubes and materials for coolers where seawater is used as cooling medium, there is obtained an excellent corrosion resistance against seawater as well as against common corrosion and against the tendency to dezincification and stress corrosion.

Thus, the seawater-resistant brass or aluminum-brass alloy of the present invention having at least 62 percent copper, at least 10 percent zinc and from 0 to 4 percent aluminum, preferably for pipe, sheet, band or wire material, particularly condensator tubes and materials for coolers where seawater is used as cooling medium, is characterized by an iron content of about 0.06 to 4 percent by weight.

By employing brass alloys having such relatively high iron contents there are formed corrosion-resistant iron compounds on the surfaces of the objects prepared, and a closer examination of the surface layers shows the presence of copper-iron magnetites which probably constitute an important factor in the corrosion-resistant film cons titutent.

An alloy containing 76 percent copper, 2 percent aluminum, and 0.04 percent arsenic and with a varying content of iron and balance zinc increases the durability against stress corrosion threefold when the iron content is increased from 0.02 percent to 1.74 percent in case of stresses giving large plastic deformation and under the influence of ammonia vapor. In case of stresses giving a small plastic deformation (below 0.2 percent) the durability is increased tenfold by increasing the iron content from 0.02 percent to 1.34 percent, under the influence of seawater containing ammonia.

What I claim is:

1. A seawater-resistant aluminum alpha brass alloy suitable for plastic deformation for use as pipe, sheet, band, wire, and especially for condenser tubes and material for coolers where seawater is used as a cooling medium which consists essentially, by weight, of at least 10% of zinc, up to 4% of aluminum, 0.06 to 4% of iron, and the balance being copper, said copper being present in an amount of at least 62% 2. A seawater-resistant aluminum alpha brass alloy suitable for plastic deformation for use as pipe, sheet,

3 4 band, wire, andespecially for condenser tubes and ma- FOREIGN PATENTS terial for coolers where seawater is used as a cooling 468 241 9/50 Canada medium which consists essentially, by weight, of about 7047 5/87 Great Britain 76% copper, about 2% aluminum, about 0.04% arsensic, 833:288 4/60 Great Britain from 1.34 to 1.74% iron, and the balance being zinc.

OTHER REFERENCES References Cited bythe Examiner Metals Handbook 1948 Edition), published by the UNITED STATES PATENTS A.S.M., page 3 relied upon.

1,764,034 6/30 Palm 7s 1s7.5

2 400 234 5/46 Hudson 5 10 DAVID L. RECK, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 214 269 October 26, 1965 Brge Lunn It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the heading to the printed specification, after line 7, insert the following:

Claims priority, application Denmark, September 19, 1962,

Signed and sealed this 7th day of February 1967.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents 

1. A SEAWATER-RESISTANT ALUMINUM ALPHA BRASS ALLOY SUITABLE FOR PLASTIC DEFORMATION FOR USE AS PIPE, SHEET, BAND, WIRE, AND ESPECIALLY FOR CONDENSER TUBES AND MATERIAL FOR COOLERS WHERE SEAWATER IS USED AS A COOLING MEDIUM WHICH CONSISTS SESSENTIALLY, BY WEIGHT, OF AT LEAST 10% OF ZINC, UP TO 4% OF ALUMINUM, 0.06 TO 4% OF IRON, AND THE BALANCE BEING COPPER, SAID COPPER BEING PRESENT IN AN AMOUNT OF AT LEAST 62%. 